The article is a continuation of a set of the author’s previous publications about the reliability of the microprocessorbased protective devices. The statistical data introduced by the author, coincide with data of other authors and confirm higher reliability of electromechanical relays in comparison with microprocessor-based. The inadequacy of the criterion for estimating the reliability of the protective relay is noted and a new normalized criterion for such estimation is offered by author.

microprocessor-based protective devices, reliability, relay protection, life expectancy, intensity of failures, failure rate